// Copyright (c) 2013 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#ifndef NET_DNS_MDNS_CACHE_H_
#define NET_DNS_MDNS_CACHE_H_

#include <map>
#include <memory>
#include <string>
#include <vector>

#include "base/callback.h"
#include "base/macros.h"
#include "base/time/time.h"
#include "net/base/net_export.h"

namespace net {

class ParsedDnsRecord;
class RecordParsed;

// mDNS Cache
// This is a cache of mDNS records. It keeps track of expiration times and is
// guaranteed not to return expired records. It also has facilities for timely
// record expiration.
class NET_EXPORT_PRIVATE MDnsCache {
public:
    // Key type for the record map. It is a 3-tuple of type, name and optional
    // value ordered by type, then name, then optional value. This allows us to
    // query for all records of a certain type and name, while also allowing us
    // to set records of a certain type, name and optionally value as unique.
    class Key {
    public:
        Key(unsigned type, const std::string& name, const std::string& optional);
        Key(const Key&);
        Key& operator=(const Key&);
        ~Key();
        bool operator<(const Key& key) const;
        bool operator==(const Key& key) const;

        unsigned type() const { return type_; }
        const std::string& name() const { return name_; }
        const std::string& optional() const { return optional_; }

        // Create the cache key corresponding to |record|.
        static Key CreateFor(const RecordParsed* record);

    private:
        unsigned type_;
        std::string name_;
        std::string optional_;
    };

    typedef base::Callback<void(const RecordParsed*)> RecordRemovedCallback;

    enum UpdateType {
        RecordAdded,
        RecordChanged,
        RecordRemoved,
        NoChange
    };

    MDnsCache();
    ~MDnsCache();

    // Return value indicates whether the record was added, changed
    // (existed previously with different value) or not changed (existed
    // previously with same value).
    UpdateType UpdateDnsRecord(std::unique_ptr<const RecordParsed> record);

    // Check cache for record with key |key|. Return the record if it exists, or
    // NULL if it doesn't.
    const RecordParsed* LookupKey(const Key& key);

    // Return records with type |type| and name |name|. Expired records will not
    // be returned. If |type| is zero, return all records with name |name|.
    void FindDnsRecords(unsigned type,
        const std::string& name,
        std::vector<const RecordParsed*>* records,
        base::Time now) const;

    // Remove expired records, call |record_removed_callback| for every removed
    // record.
    void CleanupRecords(base::Time now,
        const RecordRemovedCallback& record_removed_callback);

    // Returns a time less than or equal to the next time a record will expire.
    // Is updated when CleanupRecords or UpdateDnsRecord are called. Returns
    // base::Time when the cache is empty.
    base::Time next_expiration() const { return next_expiration_; }

    // Remove a record from the cache.  Returns a scoped version of the pointer
    // passed in if it was removed, scoped null otherwise.
    std::unique_ptr<const RecordParsed> RemoveRecord(const RecordParsed* record);

private:
    typedef std::map<Key, std::unique_ptr<const RecordParsed>> RecordMap;

    // Get the effective expiration of a cache entry, based on its creation time
    // and TTL. Does adjustments so entries with a TTL of zero will have a
    // nonzero TTL, as explained in RFC 6762 Section 10.1.
    static base::Time GetEffectiveExpiration(const RecordParsed* entry);

    // Get optional part of the DNS key for shared records. For example, in PTR
    // records this is the pointed domain, since multiple PTR records may exist
    // for the same name.
    static std::string GetOptionalFieldForRecord(const RecordParsed* record);

    RecordMap mdns_cache_;

    base::Time next_expiration_;

    DISALLOW_COPY_AND_ASSIGN(MDnsCache);
};

} // namespace net

#endif // NET_DNS_MDNS_CACHE_H_
